1. Field of the Invention
The present invention relates to an engine having a gas-fuel injection valve for injecting or supplying gas fuel, and more particularly to a stuck-open failure detection system for detecting a stuck-open failure of the gas-fuel injection valve (failure that the valve is struck in an open state and cannot be returned to a closed state).
2. Description of the Related Art
In recent years, for the purpose of achieving lower emission, developments of a vehicle equipped with an engine using gas fuel, such as compressed natural gas, compressed propane gas or compressed hydrogen gas, have been accelerated. In the engine using gas fuel, due to properties of gas fuel, such as significantly larger bulk ratio and higher combustion speed as compared with those of gasoline, it is more difficult to ensure an air intake quantity and control a gas-fuel supply quantity. Moreover, if new gaseous hydrogen is added to an intake system having residual gaseous hydrogen during engine start, a resulting air-fuel mixture having an excessively increased hydrogen concentration is likely to cause the phenomenon that the air-fuel mixture is burnt in the intake system or the phenomenon (so-called “afterburn”) that exhaust gas containing unburnt gaseous hydrogen is burnt in an exhaust system. As one of measures against these problems, it has been proposed to interpose a shutoff valve in a hydrogen supply passage on an upstream side of a gas-fuel injection valve and close the shutoff valve at engine stall so as to avoid occurrence of backfire and afterburn, as disclosed, for example, in Japanese Patent Laid-Open Publication No. 05-214937.
Further, in the engine using gas fuel, a gas-fuel injection valve for injecting and supplying gas fuel into a combustion chamber is likely to have a failure that the gas-fuel injection valve is stuck in an open state and cannot be returned to a closed state (hereinafter referred to as “stuck-open failure”). This stuck-open failure causes gas fuel leakage to the combustion chamber, and the gas fuel leaked to the combustion chamber could be factors causing backfire or afterburn if it flows into an intake system or an exhaust system. Thus, such gas fuel leakage must be prevented by adequately monitoring a state of the gas-fuel injection valve to detect a stuck-open failure thereof. As one conventional example of a method for detecting a stuck-open failure of a gas-fuel injection valve, Japanese Patent Laid-Open Publication No. 2001-41106 proposes a method which comprises closing a shutoff valve interposed in a gas-fuel supply passage immediately after engine stop, detecting in the gas-fuel supply passage a pressure P1 just after shutoff of the shutoff valve and a pressure P2 at a time when a given time has elapsed after shutoff of the shutoff valve, and if a pressure difference (P1-P2) is equal to or greater than a predetermined value, determining that a stuck-open failure occurs in the gas-fuel injection valve.
In the above type of engine, a pressure in a gas-fuel supply passage is apt to fluctuate along with consumption of gas fuel. Thus, when a pressure P1 in the gas-fuel supply passage is detected just after a shutoff valve interposed in the gas-fuel supply passage is closed in response to engine stop, the pressure P1 is likely to have a small value depending on timing of the detection. In this case, a pressure difference (P1-P2) between the pressure P1 and a pressure P2 detected after a lapse of a given time becomes smaller, and therefore a stuck-open failure of a gas-fuel injection valve cannot be adequately detected if any. Moreover, the detection of a stuck-open failure is performed at the timing of engine stop, and this is likely to cause delay in detection of the failure.
In view of the above conventional technical problems, it is an object of the present invention to provide a stuck-open failure detection system for a gas-fuel injection valve, capable of adequately detecting a stuck-open failure of the gas-fuel injection valve to prevent gas fuel from leaking into a combustion chamber while avoiding occurrence of abnormal combustion, such as backfire and afterburn.